Burdoin tubing in degassing and pulsation dampener application

ABSTRACT

A flow-dampening degassing apparatus for transport of liquid chromatography fluids therethrough includes a substantially burdoin-shaped flexible tube disposed in a reduced-pressure chamber, the tube being sufficiently flexible to expand in a cross-sectional direction upon incursion of a fluid pulsation to thereby increase an inner volume of the tube and correspondingly reduce fluid pressure therein. In a particular embodiment, the tube is fabricated from a gas-permeable and liquid-impermeable material for degassing transported fluids in the reduced-pressure chamber.

FIELD OF THE INVENTION

[0001] The present invention relates to vacuum degassing andpulse-dampening systems generally, and more particularly to vacuumdegassing, pulse-dampening systems for use in liquid chromatographyapplications. This invention also relates to methods for dampening flowpulsations and degassing mobile phase materials.

BACKGROUND OF THE INVENTION

[0002] A variety of applications exist today involving the use of fluidsolvents or reactants, wherein the presence of dissolved gases,particularly air, is undesirable. One example of such an applicationrelates to mobile phases in high performance liquid chromatography,where the presence of even small amounts of dissolved gases caninterfere with the accuracy and sensitivity of the results obtained. Insome cases, the dissolved gases can form bubbles in the mobile phase,thereby causing measurement error in chromatographic applications.Furthermore, some dissolved gases can cause deleterious effects on themobile phase as well as the surrounding componentry. Often times, suchdetrimental effects caused by the dissolved gases is related to therelative concentration of the gases in the mobile phase. To avoid sucheffects, the gases are typically removed from the mobile phase through aknown degassing process.

[0003] An additional issue that exists in present liquid chromatographysystems involves the necessity of dampening fluid pressure pulsationsflowing through respective flow conduits and through respectivechromatographic columns, which pulsations result from uneven draw anddischarge from positive-displacement fluid pumps, such as reciprocatingpumps. To obtain the most accurate chromatographic measurementspossible, fluid (mobile phase) flow through the column and the detectorshould be nearly constant. Thus, in order to obtain a continuous fluidflow at a substantially constant rate, it is desirable to provide thechromatographic system with a pulse-dampener in the fluid flow conduitbetween the fluid pump and the column/detector.

[0004] Fluid pressure pulsations in liquid chromatography systems mayalso occur upstream from respective fluid pumps, thereby adverselyaffecting chromatographic operations upstream from the fluid pump. Inmany applications, the mobile phase transported through the liquidchromatography system is a blend of multiple solvents. In suchembodiments, individual solvent reservoirs are operably connected to ablending valve apparatus to blend desired quantities of the distinctsolvents into a unitary mobile phase. Solvent may be drawn from therespective reservoirs into the blending valve apparatus by a downstreamfluid pump, which pump subsequently delivers the blended mobile phase tothe remaining chromatographic components. Because of the pulsationcharacteristics of the fluid pump, it is desirable to provide mechanismsfor dampening such pulsations between the respective solvent reservoirsand the blending valve apparatus, as well as downstream from theblending valve apparatus. Fluid flow pulsations drawn into the blendingvalve apparatus have the tendency to decrease the accuracy of theblended mobile phase, such that desired ratios of respective solventscomprising the blend may not be accurate. Further, fluid flow pulsationsinto the blending apparatus can negatively effect physical componentryin the blending valve apparatus, and may decrease the overall lifeexpectancy thereof. It is therefore desirable to provide apulse-dampening characteristic to the fluid flow conduits connectingsuch chromatographic components, and particularly between respectivefluid reservoirs and a mobile phase blending apparatus.

[0005] A number of pulse-dampening techniques have been implemented toprovide such flow-dampening characteristics in liquid chromatographyapplications. For example, fluid has been routed into expandablechambers, wherein a sudden influx of fluid pressure causes theexpandable chamber to correspondingly expand, thereby increasinginternal volume and absorbing excess fluid pressure to maintain arelatively constant fluid pressure downstream of the expandable chamber.Such flow-dampening devices, however, can result in non-laminar flowpatterns, which may result in detrimental formation of gas bubbles inthe bulk of the mobile phase. As described above, such gas bubbles caninterfere with accurate chromatographic analysis.

[0006] Other proposed systems provide dead volumes in the fluid flowpathways, which volumes are not completely filled in standard flowregimes. Upon fluid flow pulsations, however, the dead volumesaccumulate the excess fluid flow, thereby mitigating the flow impactdownstream of the dead volumes. As with the expandable chambers,however, the dead volumes may act to promote non-laminar flow in thefluid conduits.

[0007] Some applications utilize elliptical or flattened tubes aspulse-dampening fluid conduits. Such pulse-dampening tubes aresufficiently flexible to change in cross-sectional profile when a fluidpulse is directed through the tubes. Typical such applications, however,surround the flexible tubing with restraining means for limiting theextent of cross-sectional distention. Such restraining means act againstchange in cross-sectional profile of the fluid conduits so that thefluid conduits return to an elliptical or flattened profile after thefluid pulse has been dampened. Such restraining means include biasingmeans, external bodies, and compressible fluids surrounding the fluidconduits.

[0008] In addition, the flow-dampening systems proposed to date fail toaddress the degassing issue in liquid chromatography applications asdescribed above. A particular method of degassing mobile phases includesthe use of semi-permeable synthetic polymer resin materials as a fluidconduit material, and the exposure of such a semi-permeable conduit to areduced pressure or vacuum environment. To perform the degassing, thefluid to be degassed is caused to flow through the conduit in thereduced pressure environment, which allows the dissolved gases to escapefrom the mobile phase through the semi-permeable conduit walls. Byaddressing both the degassing functions and the flow-dampening functionsin a single apparatus, increased chromatographic efficiency andreduced-sized chromatographic instruments may be achieved.

[0009] Accordingly, it is a principle object of the present invention toprovide a means for simultaneously degassing a mobile phase anddampening pulsations in such a mobile phase using one or moresemi-permeable tubes.

[0010] A further object of the present invention is to provide a fluidpulse-dampening apparatus having degassing capabilities.

[0011] A still further object of the present invention is to provide asubstantially burdoin-shaped flexible tube for dampening flow pulsationsand for degassing fluids passing therethrough.

[0012] A yet further object of the present invention is to provide asubstantially burdoin-shaped flexible tube in a reduced-pressure chamberfor degassing fluids passing through the tube, which tube further actsto dampen fluid pulsations passing therethrough.

[0013] Another object of the present invention is to provide aflow-dampening degassing apparatus capable of withstanding fluidpulsations of up to about 100 pounds per square inch.

[0014] A still further object of the present invention is to provide afluid pulse-dampening apparatus having fluid degassing capabilities,wherein the apparatus is substantially configured to maintain laminarfluid flow therewithin.

SUMMARY OF THE INVENTION

[0015] By means of the present invention, an apparatus forsimultaneously dampening fluid flow pulsations and degassing fluidspassing through a semi-permeable tube is provided. This is achieved byforming the tube in a substantially burdoin-shaped configuration, withthe tube being fabricated from a gas-permeable and liquid-impermeablematerial such as an amorphous perfluorinated copolymer. Through the useof such amorphous perfluorinated copolymers, tubes having sufficientflexibility to extend in a cross-sectional direction for fluid flowpulse-dampening characteristics may be fabricated without compromisingfluid degassing characteristics. Through such an apparatus, designefficiency of liquid chromatography applications is enhanced bycombining flow-dampening and degassing functionality into one apparatus,as described in the present application.

[0016] One embodiment of the flow-dampening degassing apparatus of thepresent invention includes a substantially burdoin-shaped flexible tubedisposed in a chamber, which chamber is preferably operably coupled to avacuum source such that the chamber has a reduced internal pressure. Thetube is preferably sufficiently flexible to expand in a cross-sectionaldirection upon incursion of a fluid pulsation to thereby increase aninner volume and correspondingly reduce fluid pressure therein, whilealso being sufficiently resilient to return to its originalconfiguration after the pulse has been dampened. The tube is operablycoupled to a fluid pump, which pump may render fluid flow pulsationsboth upstream and downstream therefrom. The tube is preferably agas-permeable and liquid-impermeable material, and is more preferably anamorphous perfluorinated copolymer such as TEFLON AF™. The tubepreferably has a wall thickness of between about 0.002 inches and about0.010 inches, such that the tube can effectively dampen fluid pulsationsof up to about 100 pounds per square inch. Such an embodiment of theflow-dampening degassing apparatus is preferably utilized in conjunctionwith a high performance liquid chromatography system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic diagram showing a flow-dampening degassingapparatus of the present invention.

[0018]FIG. 2 is a cross-sectional view of the flow-dampening degassingapparatus illustrated in FIG. 1.

[0019]FIG. 3 is a cut-away cross-sectional side view of theflow-dampening degassing apparatus illustrated in FIG. 2.

[0020]FIG. 4 is a cross-sectional view of an alternative embodiment of aflow-dampening degassing apparatus of the present invention.

[0021]FIG. 5 is a cut-away cross-sectional end view taken along cut line5 of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The objects and advantages enumerated above together with otherobjects, features and advances represented by the present invention willnow be presented in terms of detailed embodiments described withreference to the attached drawing figures which are intended to berepresentative of various possible configurations of the invention.Other embodiments and aspects of the invention are recognized as beingwithin the grasp of those having ordinary skill in the art.

[0023] Referring now by characters of reference to the drawings andfirst to FIG. 1, a flow-dampening degassing system 10 is shown.Flow-dampening degassing system 10 preferably includes a vacuum chamber12 which is operably coupled to a vacuum pump 14, which pump 14 servesas a vacuum source to reduce internal pressure within vacuum chamber 12.In the embodiment shown in FIG. 1, flow-dampening degassing system 10further includes a vacuum sensor 20 operably coupled to vacuum chamber12, and electronic control means 16 operably coupled to vacuum pump 14and to vacuum sensor 20, and an operator interface 18 operably coupledto control means 16.

[0024] Vacuum chamber 12 may be embodied in a variety of configurations,and is illustrated in FIG. 1 as a representative embodiment of suchvacuum chambers. As can be seen more clearly in FIG. 2, vacuum chamber12 is preferably manufactured from a high-impact polymer material, suchas high density polyethylene or polypropylene, which can be readilyassembled with sealing o-rings or heat welded together to form a strong,relatively inert, non-metallic housing 21. As shown in FIG. 2, aflow-dampening degassing tube 22 may be wound about a central shaft orspool member 24 to form a coil. In such a manner, a relatively largeamount of flow-dampening degassing tube 22 is exposed to the reducedpressure environment within vacuum chamber 12, thereby providing anefficient means for degassing and pulse-dampening fluids passing throughtube 22. Flow-dampening degassing tube 22 preferably extends between aninlet connection 26 and an outlet connection 28. Vacuum chamber 12preferably further includes a vacuum connection 30 for connection to avacuum source, preferably vacuum pump 14.

[0025] Flow-dampening degassing tube 22 is preferably a semi-permeablepolymeric material. In preferred embodiments, flow-dampening degassingtube 22 is a gas-permeable and liquid-impermeable material such as anamorphous perfluorinated copolymer. An example of such an amorphousperfluorinated copolymer is TEFLON AF™ 2400 manufactured by E. I. duPont de Nemours and Company. TEFLON AF™ is a preferred material for usein flow-dampening degassing tube 22 for its desirable degassing andinertness characteristics. TEFLON AF™, when manufactured to desired wallthicknesses, is also sufficiently flexible to perform the flow-dampeningfunctions described herein.

[0026] Inlet and outlet connections 26, 28 preferably include a shortlength of interface tubing 34 which may be high strength, high density,relatively inert material, such as PEEK or, if metal, titanium orstainless steel, and having an end as at 36 over which flow-dampeningdegassing tube 22 is fitted. In preferred embodiments, interface tube 34may be connected using an appropriate sealing ferrule 38 which may beTEFZEL or other high impact inert material used in conjunction with anut 40 to connect interface tube 34 to bulkhead union 42.

[0027] As is shown in the cut-away side view of FIG. 3, flow-dampeningdegassing tube 22 is substantially burdoin shaped, thereby being largerin a first cross-sectional dimension than in a second cross-sectionaldimension. Such a preferred configuration of flow-dampening degassingtube 22 allows tube 22 to expand in a direction along the secondcross-sectional dimension, thereby increasing the internal volume oftube 22 upon incursion of a fluid pulsation. By increasing the internalvolume within tube 22, internal fluid pressure is correspondinglydecreased, and the fluid pulsation thereby dampened. Once the fluidpulsation has been dampened, resiliency in tube 22 causes the tube toregain its original, substantially burdoin-shaped configuration.Flow-dampening degassing tube 22 preferably has a wall thickness ofbetween about 0.002 inches and about 0.010 inches, though a variety oftube wall thicknesses may be employed to handle various expectedinternal fluid pressures and fluid pulsations. In preferred embodiments,however, tube 22 is capable of handling and dampening flow pulsations ofup to about 100 pounds per square inch. If greater wall thicknesses areutilized in tube 22, however, larger fluid pulsation pressures may beeffectively dampened.

[0028] In some embodiments, inlet connection 26 is downstream from afluid pump (not shown) whereby vacuum chamber 12 is preferably disposedbetween a fluid pump and downstream components, which components areoperably coupled to outlet connection 28. In a particularly preferredembodiment, vacuum chamber 12 is utilized in conjunction with ahigh-performance liquid chromatography system, wherein a mobile phase ispumped through flow-dampening degassing tube 22 in vacuum chamber 12,and into a chromatographic column for analysis of such mobile phase.

[0029] Another embodiment of the present invention is illustrated inFIG. 4, wherein an in-line vacuum chamber 61 is shown. Flow-dampeningdegassing system 60 includes a flow-dampening degassing tube 62, whichis preferably disposed between various liquid chromatography systemcomponents, including those upstream from said pump. Flow-dampeningdegassing tube 62 preferably extends between opposite ends 64 and 66,and is disposed in interior portion 68 of vacuum chamber 61.

[0030] Vacuum chamber 61 is preferably PEEK, but may be any highstrength, relatively inert material. Vacuum chamber 61 may be sealed atends 70 and 72 through the use of PTFE/FEP dual-shrink tubing 71, 73which is disposed in surrounding relationship to tube 62. Preferably, apair of nuts 74, 76 in conjunction with a pair of ferrules 78, 80 areformed in surrounding relationship to tubing 71, 73 for connectingvacuum chamber 61 between respective liquid chromatography systemcomponents. As shown in FIG. 4, a vacuum adapter 82 is provided forcommunication between interior portion 68 of vacuum chamber 61 and avacuum source (not shown) to evacuate interior portion 68.

[0031]FIG. 5 is a cross-sectional end view taken along line 5 shown inFIG. 4. As illustrated in FIG. 5, flow-dampening degassing tube 62 ispreferably substantially burdoin-shaped such that a firstcross-sectional dimension is larger than a second cross-sectionaldimension. As described herein, such a preferred configuration providesdesired flow-dampening characteristics.

[0032] The flow-dampening degassing tube of the present inventionpreferably simultaneously acts to degas fluids flowing therethrough andto dampen fluid flow pulsations. In preferred embodiments, theflow-dampening degassing tube is disposed in a reduced-pressure vacuumchamber to provide desired degassing functionality. In such a manner,the distinct functions of degassing and flow-dampening, which areimportant to liquid chromatography applications, may be combined in asingle apparatus as in the present invention. By combining suchfunctions, liquid chromatography systems may be fabricated in a morecompact and efficient manner.

[0033] In use, the flow-dampening degassing apparatus of the presentinvention degasses fluids passing therethrough and dampens fluidpressure pulsations incurred therein. The flow-dampening degassing tubepreferably conducts fluid driven by a fluid pump, which pump may bepositive displacement type fluid pump. Thus, the flow-dampeningdegassing tube may be operably coupled to the fluid pump inlet oroutlet, or may be disposed remotely from the pump. In particular, thetube of the present invention is preferably utilized between respectivesolvent reservoirs and a blending valve apparatus, as well as betweenthe blending valve apparatus and downstream chromatographic components.

[0034] In many of such pumps, fluid flow deviations occur on asemi-regular basis. Therefore, fluid flow pulsations are quite typicalin such applications. To enhance measurement accuracy in liquidchromatography applications, the flow-dampening degassing tube ispreferably temporarily expandable in a cross-sectional direction toincrease the volume within the tube, and thereby decrease fluid pressuretherein. In practice, the fluid pulsation causes the flow-dampeningdegassing tube to momentarily expand, which acts to dampen such a fluidflow pulse. Once the pulse has been dampened, residual resilient forcesin the flow-dampening degassing tube act to reconfigure the tube in asubstantially burdoin-shaped configuration, thereby readying the tubefor a subsequent fluid flow pulsation. The net effect of such dampeningis to normalize the fluid flow exiting the flow-dampening degassingapparatus so that chromatographic instruments downstream of theflow-dampening degassing apparatus receive a relatively constant flowrate of fluid.

[0035] The invention has been described herein in considerable detail inorder to comply with the patent statutes, and to provide those skilledin the art with the information needed to apply the novel principles andto construct and use embodiments of the invention as required. However,it is to be understood that the invention can be carried out byspecifically different devices and that various modifications can beaccomplished without departing from the scope of the invention itself.

What is claimed is:
 1. A flow-dampening degassing apparatus for transport of liquid chromatography fluids therethrough, said flow-dampening degassing apparatus comprising: a substantially burdoin-shaped flexible tube disposed in a chamber, said chamber being operably coupled to a vacuum source such that said chamber has a reduced internal pressure, said tube being sufficiently flexible to expand in a cross-sectional direction upon incursion of a fluid pulsation to thereby increase an inner volume of said tube and correspondingly reduce fluid pressure therein.
 2. A flow-dampening degassing apparatus as in claim 1 wherein said tube comprises a gas-permeable and liquid-impermeable material.
 3. A flow-dampening degassing apparatus as in claim 2 wherein said tube comprises an amorphous perfluorinated copolymer.
 4. A flow-dampening degassing apparatus as in claim 1 wherein said tube has a wall thickness of between about 0.002 inches and about 0.010 inches.
 5. A flow-dampening degassing apparatus as in claim 4 wherein said tube effectively dampens fluid pulsations of up to about 100 pounds per square inch.
 6. A flow-dampening degassing apparatus as in claim 1 wherein said tube is operably coupled to a fluid pump outlet.
 7. A flow-dampening degassing apparatus as in claim 1 wherein the fluid is a mobile phase used in high performance liquid chromatography applications.
 8. A flow-dampening degassing apparatus as in claim 1 wherein said tube is sufficiently resilient to return to the substantially burdoin-shaped configuration after the fluid pulsation has been dampened.
 9. A flow-dampening degassing apparatus as in claim 1 wherein said tube is operably disposed between one or more fluid reservoirs and a blending valve apparatus. 